Going by past auctions, DreamTR's experiences, and general past discussions, you can safely appraise just about any condition gold cart for $5000, as long as it isn't in absolutely horrendous condition. And honeslty, that's probably exactly what they average...$5000 when sold.
Iirc, one sold for near 8k once, but I don't have any saved record of it. I don't reccomend paying over $6500 for one, as you'd be getting a super-shitty deal. I'd offer the average 5k as a maximum bidding amount and leave it at that.
BTW, get pics before you buy. Really good, hi-res pics (gold carts are not numbered like the grays and can only be uniquely identified by their label placement and and other artifacts like tiny scratches and such on the cart), as you don't want someone waving around stock pics that have been floating around the net. You dont want to fuck around with a purchase like this and it should be inspected by some of us to ensure authenticity. On a selfish note, I want the pics to document the cart
...still plugging away at documenting all things NWC...I really do hope I get enough info to write the book I want to write about the event...getting there, but slowly. Got a lot of interviews and other info, but it's slow work.
-Rob